In the course of treating and preparing subterranean wells for production, a well packer and screen along with a service tool are run into the well on a work string, with the packer being set against a casing bore.
It is necessary to manipulate the service tool within the well to set, position or release downhole equipment. The success of such operations is dependent upon the ability to reciprocate the tool vertically or to rotate it relative to the downhole equipment. Rotational displacement of the tool in deviated wells is difficult to perform reliably because of frictional binding between the work string and the well casing. Accordingly, up and down reciprocal movements are preferred for setting and releasing downhole equipment in such instances.
During run-in, the packer is mechanically locked in the unset condition by shear pins. The shear pins support the weight of the packer along with the hang weight of other components such as a swivel shear sub, blank pipe, sand screen, polished nipple, tail screen, sealing unit and sump packer. The shear pins can safely support the combined weight of the downhole equipment, and are rated to yield to a preset shearing force to separate and release the service unit after the packer has been set. In deviated or otherwise obstructed well bores, the shear pins may be damaged and the packer may sometimes be inadvertently preset in response to frictional loading between the packer and the well bore in tight spots.